In the field of maintaining goods at a defined temperature which is below environmental temperature, in particular for maintaining goods so as to be cold or frozen, especially during transport, several different solutions have been proposed in the prior art. Some of these comprise the use of vehicles with integrated freezers or refrigerators. Other solutions are based on the use of thermally insulated containers, supplied with solid CO2, as is the case in the present invention.
EP1326046 B1 (Yara International ASA) discloses a multi-coupling system for filling containers, in particular thermally insulated containers, to be supplied with a cryogenic medium such as solid CO2 (commonly known as dry ice), with liquid CO2, injected from a liquid source, and which is converted into solid CO2 upon injection. Typically, a specifically dedicated inner part of such thermally insulated containers comprises a compartment or cell that is dedicated to contain the cryogenic medium, e.g., solid CO2, by separating it from the product transported inside the thermally insulated container.
The amount of solid CO2 to be supplied to a container is typically calculated based on the required residence time of the loaded one or more products to be maintained at a defined temperature, below a defined temperature, or within a defined temperature range, which temperature or temperature range is below environmental temperature. Consequently, the residence time is the time the one or more loaded products are to be maintained in the container at a defined temperature, below a defined temperature, or within a defined temperature range, which temperature or temperature range is below environmental temperature, e.g., during transport of the container. Typical residence times are 12 hours up to 3 days (i.e., over a weekend, from a Friday morning until a Monday morning), or even longer.
When performing the filling of the container with CO2, in the prior art, it is mentioned that the amount of solid CO2 to be generated is based on the duration of the injection of the liquid CO2. This is a fairly inaccurate method. When the liquid CO2, which is stored in a refrigerated form, expands into the cold cell located in the container, this cold cell being specially developed for this purpose, approximately 50-60% of the injected quantity becomes dry ice and approximately 40-50% becomes gaseous CO2, depending on the pressure within this cold cell. The gaseous CO2 produced on injection, i.e., 40-50% of the total injected quantity, is extracted via suitable devices in order to prevent an impermissible concentration of the CO2 in the atmosphere of the working premises.
Therefore, the prior art method of determining the amount of solid CO2 that is actually supplied to a container upon injection of liquid CO2 will give rise to large uncertainties due to, for example, pressure and temperature variations during the filling operation.
As soon as the desired quantity of liquid CO2 is injected into the cooling container, the CO2 filling process is automatically stopped by a timer in control thereof.
Furthermore, the prior art method will not provide identification and traceability of relevant data for a container filled with CO2.
Consequently, there exists the need to provide a more accurate way of supplying an amount of solid CO2 to a thermally insulated container.